The present invention relates to an electrostatic copying apparatus having an automatic document feed (ADF) system. More specifically, an original document is fed onto a glass platen for imaging in a first direction in such a manner that the center of the document is aligned with a center line of the document feed path regardless of the width of the document. The document is scanned perpendicular to the first direction to form an electrostatic image on a photoconductive drum. The electrostatic image is developed to form a toner image. A copy sheet is fed in a second direction which is perpendicular to the first direction into engagement with the drum to transfer the toner image to the copy sheet. The toner image is fixed to the copy sheet to provide a permanent reproduction of the original document.
It is desired to be able to copy documents having different widths (perpendicular to the center line of the document feed path). Assuming that the apparatus is arranged to copy a document having a maximum width, the leading edge of the copy sheet will align with the leading edge of the toner image on the drum during toner image transfer. However, if a document having a width which is 2.DELTA.S smaller than the maximum width is copied without modification of the system, the leading edge of the copy sheet will not align with the leading edge of the toner image on the drum. More specifically, there will be a blank space having a width of .DELTA.S extending from the leading edge of the copy sheet to the leading edge of the toner image on the copy sheet. Assuming that the width of the copy sheet is the same as the width of the document, a portion of the trailing edge of the toner image having a width of .DELTA.S will not be transferred to the copy sheet but will remain on the drum. The reasons for this are that the center of the document is aligned with the center line of the document feed path and that the imaging and transfer feed operations are performed perpendicular to the document feed operation.
One method of overcoming this problem is to vary the feed rate of the copy sheet so that the feed rate or speed is lower for small documents. However, this requires a variable transmission or other speed variation means which adds to the cost and complexity of the apparatus.
Another expedient is to align a side edge of the document with an edge of the platen. While this will align the leading edges of the copy sheet and toner image, it will produce skew feed of the document where feed rollers are provided along the center of the document feed path. Although the feed rollers may be moved transversely to align with the center of the document, a mechanism for providing this function is undesirably complex and costly.